1. Field of the Invention
The present invention relates generally to a process for bleaching cellulosic materials, such as cotton and cotton blends and, more particularly, to a rapid bleaching process for textile articles using a solution of hydrogen peroxide, potassium hydroxide and stabilizers to produce goods which are soft, absorbent, mote-free, and have excellent whiteness values.
2. Description of the Prior Art
The history of bleaching dates back to the Romans who burned sulfur inside their wool tents to produce sulfur dioxide. The valence of sulfur was supplied by wool when oxygen was removed from it. This process was not very effective because over time the wool would regain its natural yellow color by regaining the oxygen lost by reduction process.
Today, the most common type of bleaching process is the oxidation method. This process involves contributing oxygen to the textile material which would result in permanent whiteness. The most common chemicals used in oxidation processes are listed below:
(1) Sodium hypochlorite
(2) Hydrogen peroxide
(3) Peracetic acid
(4) Sodium chlorite
Of the above four types, hydrogen peroxide is rapidly gaining in popularity because it is nonyellowing, nontoxic, and odorless. In addition, hydrogen peroxide does not have the effluent problem that is associated with chlorine bleaching. For example, during chlorine bleaching, there are chlorinated hydrocarbons formed which increase the BOD and COD levels.
It is well known that simple solutions of hydrogen peroxide are ineffective in bleaching with out additives. However, alkaline solutions of hydrogen peroxide produce too fast a rate of decomposition and thus must have a stabilizer to control the rate of hydrogen peroxide decomposition. For example, U.S. Pat. No. 4,363,699 teaches bleaching textile fabrics with hydrogen peroxide, sodium hydroxide and an alphahydroxyacrylic acid polymer stabilizer and U.S. Pat. No. 4,496,472 teaches using hydrogen peroxide, an alkali hydroxide and an oligomer of phosphonic acid ester stabilizer. However, such bleaching solutions usually require 40-50 minutes to produce acceptable whiteness values.
Prior bleaching solutions also have used sodium hydroxide along with sodium silicate for stabilization of hydrogen peroxide. For example, U.S. Pat. No. 4,337,060 teaches bleaching textile fabrics with potassium orthosilicate, water and hydrogen peroxide and with the reaction products of sodium silicate and potassium hydroxide. However, silicates form insoluble calcium and magnesium complexes and create a harsh hand on textile goods which can interfere with subsequent dyeing and sewing operations.
Thus, there remains a need for a new and improved bleaching process for cotton and cotton blends which rapidly bleaches to produce excellent whiteness while, at the same time, produces goods which are soft, absorbent, and mote-free.